1. Field of the Invention
The present invention relates to a sheet supply apparatus for supplying a sheet e.g., a recording sheet, a transfer sheet, a photo-sensitive sheet, an electrostatic recording sheet, a printing sheet, OHP sheet, an envelope, a post card, an original sheet, or the like) from a sheet stacking portion to a sheet treating portion (such as a recording portion, a reading portion, a working portion, or the like) in a recording apparatus (printer) acting as an information outputting apparatus of a word processor, a personal computer and the like, or in an image forming apparatus such as a copying machine, a facsimile and the like, or in other equipment using the sheet, and a recording apparatus having such a sheet supply apparatus.
2. Related Background Art
Conventionally, in sheet supply apparatuses of this kind, a function for surely separating a single sheet from a sheet stack and a function for conveying the separated sheet straightly in a conveying direction without skew-feed, to supply the sheet to a recording portion have been requested. Further, recently, there has been requested a technique in which many kinds of sheets such as a thin sheet, a thick sheet, a post card, an envelope, a resin film sheet and the like are supplied by using a single sheet supply apparatus.
An example of a conventional technique is disclosed in the Japanese Patent Publication No. 58-6633 (1983). In this technique, a driving force of a printing cylinder is transmitted to a separation roller of a sheet supply apparatus through a one-way clutch. Upon the supply of a sheet, by rotating the printing cylinder in a reverse direction, the separation roller is rotated in a sheet supplying direction to feed out the sheet until the sheet abuts against an entrance (nip) of the printing cylinder and then is flexed in a curved fashion. In this way, a tip end of the sheet is aligned with the nip of the printing cylinder, thereby correcting the skew-feed of the sheet.
Then, when the printing cylinder is rotated in a normal direction, the rotating force of the printing cylinder is not transmitted to the separation roller due to the presence of the one-way clutch and is maintained in the stopped condition, so that the sheet is pulled into the nip of the printing cylinder by a restoring force of the sheet for returning the sheet to its initial flat condition, with the result that the sheet is conveyed to the recording portion in the straight condition.
Further, another example of a conventional technique is disclosed in the Japanese Patent Publication No. 62-38261 (1987). In this technique, a sheet fed by a pick-up roller is conveyed until a tip end of the sheet reaches a predetermined position after it passes through a contact position (nip) between a pair of drive rollers, and then, the sheet is conveyed in a reverse direction until the tip end of the sheet passes through the contact position, so that the sheet is flexed in a curved fashion between the pick-up roller and the drive rollers to abut the tip end of the sheet against the contact position, thereby correcting skew-feed of the sheet. Thereafter, when the drive rollers are rotated, the sheet is pulled between the drive rollers by a restoring force of the sheet for returning the sheet to its initial flat condition.
However, in the conventional sheet supply apparatus wherein the skew-feed of the sheet is corrected by abutting the sheet against the printing cylinder, if the tip end of the sheet does not enter into the entrance of the printing cylinder straightly (parallel with the entrance), when the tip end of the sheet impinges the printing cylinder, the sheet will be kicked back or the tip end of the sheet will be folded, thereby causing poor sheet supply.
Further, in the above-mentioned conventional sheet supply apparatuses, the skew-feed of the sheet is corrected by flexing the sheet and the sheet is pulled into the printing cylinder or the drive rollers by the restoring force of the sheet for returning the sheet to its initial flat condition, with the result that the sheet must be flexed to obtain the restoring force. However, as mentioned above, recently, since many kinds of sheets are used, for example, if the post card or the envelope is used, it will be folded when it is flexed. Thus, the kind of the sheets to be supplied is limited.